help me with php nuke..

hello.

im getting the error

Fatal error: Cannot instantiate non-existent class: sql_db in /home/www/marleyuk.freelinuxhost.com/football/html/db/db.php on line 86

i think its how i have my config.php setup

$dbhost = "freelinuxhost.com";
$dbuname = "marleyuk";
$dbpass = "password";
$dbname = "marleyuk_db";
$prefix = "nuke";
$user_prefix = "nuke";
$dbtype = "MySQL4";
$sitekey = "SdFk*fa28367-dm56w69.3a2fDS+e9";
$gfx_chk = 0;
$subscription_url = "";

can anyone see any problems with this?